1. Field of the Invention
This invention relates to an electrosurgical apparatus, in particular an electrosurgical apparatus comprising an electrode assembly including an electrode leg adapted to break and disable the apparatus upon expiration of a predetermined amount of use of the apparatus.
2. Description of the Prior Art
In electrosurgical instruments, as illustrated for example in FIG. 1, a pair of electrodes maintained at differential voltages and with dissimilar charge densities are used to conduct current to a target site to treat tissue. Treatment may include ablating, heating, cutting, removing, puncturing, probing, and otherwise stimulating tissue at the target site. The target site may include any part of a patient's body including the skin, knee, nose, spine, neck, hip, heart and the throat. See for example, U.S. Pat. No. 6,149,620 and U.S. patent application Ser. No. 09/457,201 herein fully incorporate by reference for descriptions of procedures for treating tissue at target sites using electrosurgical instruments, including procedures and instruments readily adaptable for use in accordance with the present apparatus and method.
On these instruments, the electrode with the higher charge density, referred to as the active electrode, conducts current to the target site whereas the electrode at the lower charge density, referred to as the return electrode, conducts current away from the target site. Depending on the instrument's design both electrodes may be positioned on the distal end of a shaft of the instrument in which case the instrument is referred to as a bipolar instrument. Alternatively, where only the active electrode is positioned on the shaft of the instrument and the return electrode is placed elsewhere off the instrument but in an electrical circuit with the active electrode and the target site, the instrument is referred to as monopolar instrument. In both designs, however, regardless of where the electrodes are located, for the instrument to work, it is necessary to maintain a closed electrical circuit comprising the electrodes, the target site that including a conductive media, and a high-frequency alternating voltage source.
In electrosurgical procedures, whether a monopolar or a bipolar instrument is used, treatment of the target site is effected in one of three ways: passing current through the tissue at the site; passing current through a conductive fluid on the site; or generating plasma by passing current through a conductive fluid near the target site and directing the plasma to the site. Conductive fluid includes saline and lactated ringers solution. See for example, U.S. Pat. No. 6,149,620, and U.S. patent application Ser. No. 09/457,201, supra, for description of methods of treating tissue in accordance with one or more of these procedures.
In treating a target site, an important consideration is to limit the time that the tissue is exposed to current so as to avoid unintended damage to the tissue. Another consideration is to prevent accidental reuse of disposable components of the instruments, such as the electrodes, to reduce the risk of infection. A further consideration is to avoid using an instrument having electrodes that are worn or eroded to a state such that their mechanical structures are weakened to an unacceptable level and are likely to break.
One approach to limit exposure of the tissue to excessive current, and or control wear on the electrode is to rely on the operator to monitor the time that the instrument is in use and stop treatment at an appropriate time. This may be done, for example, either manually or automatically using various timing devices on the power supply.
However, while monitoring the power supply is feasible to track the time that the tissue is exposed to current, merely monitoring the power does not indicate to the operator the extent of erosion and wear occurring on the electrodes. In this regard the applicant has discovered that as the instrument is used, the active electrode erode and wear and are likely to break. Further, depending on the material used, the dimensions of the active electrode, the type of conductive fluid used, the location of the connection to the power supply and the voltage applied to the electrodes, erosion may occur to the extent where the electrodes undesirably breaks causing bits of fragments to become lodged in the tissue. Thus, while it is possible to monitor the power to prevent over-exposure of the tissue to current, it is a problem to decide when to stop use of the instrument to avoid the undesirable consequences of erosion and wear on the electrodes and or a break on the electrodes.
One approach to monitoring the instrument for electrode erosion and wear is to visually check the physical condition of the electrodes. A problem with this approach is that because the electrodes are almost invisible to an unaided eye, it very difficult to visually determine erosion and wear. A further practical problem is that during the exigencies of a surgical procedure, a practitioner may overlook the need to periodically check the electrodes for erosion wear in time to stop using the instrument before wear becomes a problem and or the electrode breaks.
Accordingly, there is need for a more reliable way to prevent unintended and or prolonged use of the equipment, excessive exposure of the tissue to current, the consequences of a deteriorated electrode, and or the unintended reuse of disposable components of the instrument. It is thus an object of the present invention to address at least these needs.